The present invention relates to novel, highly sensitive electrodes and to methods of generating and using same in detection of a variety of molecules.
During the last few years much interest has been focused on the development of analytical methods allowing rapid “on-the-spot” performances for medical diagnostics and to measure environmental pollutants. A device operating in remote sites, such as an ambulance, an agricultural farm, or in field testing of environmental pollutants, should provide fast, sensitive, small and inexpensive measurements. Moreover, for measurements held in the field, the device should be simple to operate by a non-qualified person.
In amperometric measurements a potential is applied between a working electrode and a reference electrode and the resulting current is measured. Often a third electrode, an auxiliary electrode, is used for current collection.
The response of a working electrode depends on the chemical (electrochemical) reaction variables. These include the electrode surface where the reaction takes place, the mobile phase (reaction medium), and the compound undergoing the reaction.
Measurements are performed either at constant or varying potential between the working electrode and the reference electrode. In cyclic voltammetry the potential is changed linearly from an initial potential to a final potential and then back to the initial value, and the resulting current is measured. When an electroactive molecule is present in the tested solution, a peak is observed. The scan rate (rate of potential changed) affect the peak height and the peak position depends on kinetic constants of the electrochemical reaction.
A number of diagnostic tests are routinely performed on humans to evaluate the amount or existence of substances present in blood or other bodily fluids. These diagnostic tests typically rely on physiological fluid samples removed from a subject, either using a syringe or by pricking the skin.
Biological samples can be tested for the presence of a specific molecule by using a detector electrode capable of electrochemically reacting with the detected molecule.
Amperometric biosensors combine the specificity and selectivity of biological interaction reactions with the analytical power of electrochemistry. Many analytes are not intrinsically electroactive and cannot be detected directly. The use of enzymes that catalyze biospecific reactions facilitates the production of electroactive species which then can be determined electrochemically.
Since their discovery in 1991, carbon nanotubes (CNTs) have been extensively studied both theoretically and experimentally due to their unique physical and chemical properties. Such nano-scale tubular structures have been suggested as potential functional elements in nanotechnological devices and applications.
Kong et al. (2000) was the first to build a CNT based chemical sensor for detection of NH2 and NH3 gas. Chen et al. (2001) immobilized proteins on CNTs through a linking molecule and Besteman et al. (2003), Lin et al. (2004) and Wang et al. (2003) demonstrated the use of CNTs as biological sensors for detection of glucose. The unique electric properties together with significant surface enlargement made CNTs an important component in sensing applications.
Studies also showed that bioorganic molecules can also self-assemble into well-ordered structures at the nanometric level (Hartgerink et al. 2001; Ashkenasy et al., 2006). Biomolecular nanostructures are an especially intriguing group of supramolecular assemblies because they facilitate a wide range of chemical modifications. Moreover, such nanostructures enable exploitation of the specificity of biological systems for biosensing, catalytic activity, and highly specific molecular recognition processes.
Well-ordered and discrete peptide nanotubes that are self assembled from aromatic peptides (e.g., diphenylalanine peptides) and uses thereof in numerous mechanical, electrical, chemical, optical and biotechnological systems have recently been reported (see, for example, Reches and Gazit 2003, 2004; WO 2004/052773; WO 2004/060791; PCT/IL2005/000589; WO 2006/027780 and U.S. patent application Ser. Nos. 11/148,262 and 11/148,266, which are all incorporated by reference as if fully set forth herein).
These peptide nanotubes are biocompatible and water soluble. They show notable similarity to carbon nanotubes in their morphology and aspect ratio. Their assembly as individual entities rather then bundles, makes them appealing for various nanotechnological applications.
It has thus been envisioned that electrodes coated with peptide nanostructures could exhibit the desired characteristics required for efficient and sensitive electrochemical measurements.